I had a similar experience yesterday when adding a new butterflyfish. I have some Aptasia and brought home a butterfly that the store claimed would eat them. (We shall see if it serves that purpose, but that is another story).
My purple tang immediately went warzone on the new butterfly, who began looking out of the aquarium at me pathetically asking to take him out. I got out the fish net and chased the purple into a corner a couple of times hoping to get the battle to stop. I stepped away from the tank and instantly the battle was back on.
A little history is needed. Last week I had ventured out from my home quarantine to get frozen fish food and while I was there I had picked up a small copperband butterfly. I observed him happily swimming around the tank when I first added him and walked away unconcerned. The next day my wife asked where he was and I replied that I thought he must be hiding as I didn't see him anywhere. I looked behind and under everything and could not locate the copperband who is still MIA.
The new butterfly is much bigger than the missing copperband but it was clearly a little fish store weak (filmy scales and a few suspect spots, but nothing horrifically out of place). since I am trying to support the LFS's I decided to purchase him hoping that he would not disappear, get healthy and eat Aptasia. I brought him home and fed the fish and then let the new fish go.
It was about 3 hours before lights out when I observed that the purple tank was making full tank rushes directly at the new butterfly and bashing the newcomer with vigor. The tang was clearly hellbent upon kicking the butterfly out of the tank one way or another. The butterfly kept swimming up to the glass and looking at me for help, so I got the fish net out again and began chasing the purple tang into a corner every time it moved. I could see it wasn't getting the message because as quickly as the net came out of the water the tang would immediately flash out from where it had been hiding out and sideswipe the butterfly again at full speed, trying to rip the butterfly a new-one.
As my last-ditch effort to assert authority in the fish tank, I began pushing the net forcefully through the water, not aiming at anything in particular but causing the water to begin sloshing back and forth in the tank. I kept at this for about 30 seconds until the surface of the water was violently pitching around as if a storm had hit. Small wavelets were bursting against the sides of the tank and the water sloshed out from all 4 corners and many other places around the edge of the tank. I told the fish (again) to stop fighting, said a prayer for peace, and walked away hoping that the message would be understood.
I came back 2 hours later and fed the fish a second and third time because they were behaving well enough and the terror between fishes had stopped. I hope your fish will figure out how to have peace in your tank. I always recommend the net, or the hand if you want to encourage the fish to get along. GL